Design a Question and Answer Platform Object-Oriented Design Interview
Design a Q&A platform domain model with users, questions, answers, comments, tags, votes, an accepted-answer rule, and a reputation policy, with the voting, acceptance, and reputation invariants enforced in the model.
1. Problem Statement
Design a question-and-answer platform where users post questions and answers, add comments and tags, vote posts up or down, and the question's author accepts one answer. Reputation changes with votes and acceptance. Start by clarifying scope and the core objects.
2. Live Coding Format
Work in the provided coding workspace while explaining your decisions to the live interviewer. Validation may use inline tests, examples, comments, or a verbal walkthrough.
3. Key Focus Areas
- 1Post abstraction shared by Question and Answer
- 2Voting invariants (one per user, replace on change, no self-vote)
- 3Accepted-answer rule and authorization
- 4ReputationPolicy strategy and reputation ledger ownership
4. What Strong Candidates Should Demonstrate
- ✓Model Users, Questions, Answers, Comments, Tags, and Votes with a shared Post abstraction.
- ✓Enforce one-vote-per-user, no-self-vote, and single-accepted-answer invariants in the model.
- ✓Restrict answer acceptance to the question's author.
- ✓Encapsulate reputation changes behind a replaceable policy.
Want interactive feedback?
Practice this problem in the live coding workspace while the interviewer probes your clarification, implementation, trade-offs, and validation.
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